1,672 research outputs found
Is efficiency of classical simulations of quantum dynamics related to integrability?
Efficiency of time-evolution of quantum observables, and thermal states of
quenched hamiltonians, is studied using time-dependent density matrix
renormalization group method in a family of generic quantum spin chains which
undergo a transition from integrable to non-integrable - quantum chaotic case
as control parameters are varied. Quantum states (observables) are represented
in terms of matrix-product-operators with rank D_\epsilon(t), such that
evolution of a long chain is accurate within fidelity error \epsilon up to time
t. We find that rank generally increases exponentially, D_\epsilon(t) \propto
\exp(const t), unless the system is integrable in which case we find polynomial
increase.Comment: 4 pages; v2. added paragraph discussing pure state
Tomographic Quantum Cryptography: Equivalence of Quantum and Classical Key Distillation
The security of a cryptographic key that is generated by communication
through a noisy quantum channel relies on the ability to distill a shorter
secure key sequence from a longer insecure one. For an important class of
protocols, which exploit tomographically complete measurements on entangled
pairs of any dimension, we show that the noise threshold for classical
advantage distillation is identical with the threshold for quantum entanglement
distillation. As a consequence, the two distillation procedures are equivalent:
neither offers a security advantage over the other.Comment: 4 pages, 1 figur
Risk factors of postpartum depression and depressive symptoms: umbrella review of current evidence from systematic reviews and meta-analyses of observational studies
Background: Evidence on risk factors for postpartum depression (PPD) are fragmented and inconsistent. Aims: To assess the strength and credibility of evidence on risk factors of PPD, ranking them based on the umbrella review methodology. Method: Databases were searched until 1 December 2020, for systematic reviews and meta-analyses of observational studies. Two reviewers assessed quality, credibility of associations according to umbrella review criteria (URC) and evidence certainty according to Grading of Recommendations-Assessment-Development-Evaluations criteria. Results: Including 185 observational studies (n = 3 272 093) from 11 systematic reviews, the association between premenstrual syndrome and PPD was the strongest (highly suggestive: odds ratio 2.20, 95%CI 1.81-2.68), followed by violent experiences (highly suggestive: odds ratio (OR) = 2.07, 95%CI 1.70-2.50) and unintended pregnancy (highly suggestive: OR=1.53, 95%CI 1.35-1.75). Following URC, the association was suggestive for Caesarean section (OR = 1.29, 95%CI 1.17-1.43), gestational diabetes (OR = 1.60, 95%CI 1.25-2.06) and 5-HTTPRL polymorphism (OR = 0.70, 95%CI 0.57-0.86); and weak for preterm delivery (OR = 2.12, 95%CI 1.43-3.14), anaemia during pregnancy (OR = 1.47, 95%CI 1.17-1.84), vitamin D deficiency (OR = 3.67, 95%CI 1.72-7.85) and postpartum anaemia (OR = 1.75, 95%CI 1.18-2.60). No significant associations were found for medically assisted conception and intra-labour epidural analgesia. No association was rated as 'convincing evidence'. According to GRADE, the certainty of the evidence was low for Caesarean section, preterm delivery, 5-HTTLPR polymorphism and anaemia during pregnancy, and 'very low' for remaining factors. Conclusions: The most robust risk factors of PDD were premenstrual syndrome, violent experiences and unintended pregnancy. These results should be integrated in clinical algorithms to assess the risk of PPD
Risk factors of postpartum depression and depressive symptoms: umbrella review of current evidence from systematic reviews and meta-analyses of observational studies
BackgroundEvidence on risk factors for postpartum depression (PPD) are fragmented and inconsistent.AimsTo assess the strength and credibility of evidence on risk factors of PPD, ranking them based on the umbrella review methodology.MethodDatabases were searched until 1 December 2020, for systematic reviews and meta-analyses of observational studies. Two reviewers assessed quality, credibility of associations according to umbrella review criteria (URC) and evidence certainty according to Grading of Recommendations-Assessment-Development-Evaluations criteria.ResultsIncluding 185 observational studies (n = 3 272 093) from 11 systematic reviews, the association between premenstrual syndrome and PPD was the strongest (highly suggestive: odds ratio 2.20, 95%CI 1.81–2.68), followed by violent experiences (highly suggestive: odds ratio (OR) = 2.07, 95%CI 1.70–2.50) and unintended pregnancy (highly suggestive: OR=1.53, 95%CI 1.35–1.75). Following URC, the association was suggestive for Caesarean section (OR = 1.29, 95%CI 1.17–1.43), gestational diabetes (OR = 1.60, 95%CI 1.25–2.06) and 5-HTTPRL polymorphism (OR = 0.70, 95%CI 0.57–0.86); and weak for preterm delivery (OR = 2.12, 95%CI 1.43–3.14), anaemia during pregnancy (OR = 1.47, 95%CI 1.17–1.84), vitamin D deficiency (OR = 3.67, 95%CI 1.72–7.85) and postpartum anaemia (OR = 1.75, 95%CI 1.18–2.60). No significant associations were found for medically assisted conception and intra-labour epidural analgesia. No association was rated as ‘convincing evidence’. According to GRADE, the certainty of the evidence was low for Caesarean section, preterm delivery, 5-HTTLPR polymorphism and anaemia during pregnancy, and ‘very low’ for remaining factors.ConclusionsThe most robust risk factors of PDD were premenstrual syndrome, violent experiences and unintended pregnancy. These results should be integrated in clinical algorithms to assess the risk of PPD
The Evolution of Gamma-ray Burst Jet Opening Angle through Cosmic Time
Jet opening angles of long gamma-ray bursts (lGRBs) appear to evolve in
cosmic time, with lGRBs at higher redshifts being on average more narrowly
beamed than those at lower redshifts. We examine the nature of this
anti-correlation in the context of collimation by the progenitor stellar
envelope. First, we show that the data indicate a strong correlation between
gamma-ray luminosity and jet opening angle, and suggest this is a natural
selection effect - only the most luminous GRBs are able to successfully launch
jets with large opening angles. Then, by considering progenitor properties
expected to evolve through cosmic time, we show that denser stars lead to more
collimated jets; we argue that the apparent anti-correlation between opening
angle and redshift can be accounted for if lGRB massive star progenitors at
high redshifts have higher average density compared to those at lower
redshifts. This may be viable for an evolving IMF - under the assumption that
average density scales directly with mass, this relationship is consistent with
the form of the IMF mass evolution suggested in the literature. The jet
angle-redshift anti-correlation may also be explained if the lGRB progenitor
population is dominated by massive stars at high redshift, while lower redshift
lGRBs allow for a greater diversity of progenitor systems (that may fail to
collimate the jet as acutely). Overall, however, we find both the jet
angle-redshift anti-correlation and jet angle-luminosity correlation are
consistent with the conditions of jet launch through, and collimation by, the
envelope of a massive star progenitor
Fitness Impact of Obligate Intranuclear Bacterial Symbionts Depends on Host Growth Phase
According to text book definition, parasites reduce the fitness of their hosts whereas mutualists provide benefits. But biotic and abiotic factors influence symbiotic interactions, thus under certain circumstances parasites can provide benefits and mutualists can harm their host. Here we addressed the question which intrinsic biotic factors shape a symbiosis and are crucial for the outcome of the interaction between the obligate intranuclear bacterium Holospora caryophila (Alphaproteobacteria; Rickettsiales) and its unicellular eukaryotic host Paramecium biaurelia (Alveolata; Ciliophora). The virulence of H. caryophila, i.e., the negative fitness effect on host division and cell number, was determined by growth assays of several P. biaurelia strains. The performances of genetically identical lines either infected with H. caryophila or symbiont-free were compared. Following factors were considered as potentially influencing the outcome of the interaction: (1) host strain, (2) parasite strain, and (3) growth phases of the host. All three factors revealed a strong effect on the symbiosis. In presence of H. caryophila, the Paramecium density in the stationary growth phase decreased. Conversely, a positive effect of the bacteria during the exponential phase was observed for several host × parasite combinations resulting in an increased growth rate of infected P. biaurelia. Furthermore, the fitness impact of the tested endosymbionts on different P. biaurelia lines was not only dependent on one of the two involved strains but distinct for the specific combination. Depending on the current host growth phase, the presence of H. caryophila can be harmful or advantageous for P. biaurelia. Thus, under the tested experimental conditions, the symbionts can switch from the provision of benefits to the exploitation of host resources within the same host population and a time-span of less than 6 days
Drivers and impact of the early silent invasion of SARS-CoV-2 Alpha
SARS-CoV-2 variants of concern (VOCs) circulated cryptically before being identified as a threat, delaying interventions. Here we studied the drivers of such silent spread and its epidemic impact to inform future response planning. We focused on Alpha spread out of the UK. We integrated spatio-temporal records of international mobility, local epidemic growth and genomic surveillance into a Bayesian framework to reconstruct the first three months after Alpha emergence. We found that silent circulation lasted from days to months and decreased with the logarithm of sequencing coverage. Social restrictions in some countries likely delayed the establishment of local transmission, mitigating the negative consequences of late detection. Revisiting the initial spread of Alpha supports local mitigation at the destination in case of emerging events
Landslide susceptibility assessment using Frequency Ratio, a case study of northern Pakistan
The northern Pakistan is attributed with rough terrain, active seismicity, monsoon rains, and therefore hosts to variety of geohazards. Among the geohazards, landslides are the most frequent hazard with devastating impacts on economy and society. However, for most of the northern Pakistan, landslide susceptibility maps are not available which can be used for landslide hazard mitigation. This study aims to develop a remote sensing based landslide inventory, analysing their spatial distribution and develop the landslide susceptibility map. The area, selected for this study is comprised of Haramosh valley, Bagrote valley and some parts of Nagar valley, in the Central Karakoram National Park (CKNP) in Gilgit-Baltistan, northern Pakistan. The SPOT-5 satellite image was used to develop a landslide inventory
which was subsequently verified in the field. The landslide causative factors of topographic attributes (slope and aspect), geology, landcover, distances from fault, road and streams were used to evaluate their influence on the spatial distribution of landslides. The study revealed that the distance to road, slope gradient
has the significant influence on the spatial distribution of the landslides, followed by the geology. The derived results were used in the Frequency ratio technique to develop a landslide susceptibility map. The developed landslide susceptibility map can be utilized for landslide mitigation in the study area
Information-Theoretic Analysis of Cardio-Respiratory Interactions in Heart Failure Patients: Effects of Arrhythmias and Cardiac Resynchronization Therapy
The properties of cardio-respiratory coupling (CRC) are affected by various pathological conditions related to the cardiovascular and/or respiratory systems. In heart failure, one of the most common cardiac pathological conditions, the degree of CRC changes primarily depend on the type of heart-rhythm alterations. In this work, we investigated CRC in heart-failure patients, applying measures from information theory, i.e., Granger Causality (GC), Transfer Entropy (TE) and Cross Entropy (CE), to quantify the directed coupling and causality between cardiac (RR interval) and respiratory (Resp) time series. Patients were divided into three groups depending on their heart rhythm (sinus rhythm and presence of low/high number of ventricular extrasystoles) and were studied also after cardiac resynchronization therapy (CRT), distinguishing responders and non-responders to the therapy. The information-theoretic analysis of bidirectional cardio-respiratory interactions in HF patients revealed the strong effect of nonlinear components in the RR (high number of ventricular extrasystoles) and in the Resp time series (respiratory sinus arrhythmia) as well as in their causal interactions. We showed that GC as a linear model measure is not sensitive to both nonlinear components and only model free measures as TE and CE may quantify them. CRT responders mainly exhibit unchanged asymmetry in the TE values, with statistically significant dominance of the information flow from Resp to RR over the opposite flow from RR to Resp, before and after CRT. In non-responders this asymmetry was statistically significant only after CRT. Our results indicate that the success of CRT is related to corresponding information transfer between the cardiac and respiratory signal quantified at baseline measurements, which could contribute to a better selection of patients for this type of therapy
Increasing of entanglement entropy from pure to random quantum critical chains
It is known that the entropy of a block of spins of size embedded in an
infinite pure critical spin chain diverges as the logarithm of with a
prefactor fixed by the central charge of the corresponding conformal field
theory. For a class of strongly random spin chains, it has been shown that the
correspondent block entropy still remains universal and diverges
logarithmically with an "effective" central charge. By computing the
entanglement entropy for a family of models which includes the -states
random Potts chain and the clock model, we give some definitive answer to
some recent conjectures about the behaviour of the effective central charge. In
particular, we show that the ratio between the entanglement entropy in the pure
and in the disordered system is model dependent and we provide a series of
critical models where the entanglement entropy grows from the pure to the
random case.Comment: 4 pages, 2 eps figures, added reference
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